Device for separating particles of different masses



W. ALTAR March 31, 1953 DEVICE FOR SEPARATING PARTICLES OF DIFFERENTMASSES Filed Jan. 14, 1948' LOW Mega zfve Vo/zfaye H/yh lVeya five 75Reservoh' V0 H W of No/ecu/es INVENTOR W/'///'am 14/ tax v I 4 ATTORNBYKN Patented Mar. 31, 1953 DEVICE FOR SEPARATING PARTICLES OF DIFFERENTMASSES William Altar, Pittsburgh, Pa., assignor, by mesne assignments,to the United States of America as represented by the United StatesAtomic Energy Commission Application January 14, 1948, Serial No. 2,337

16 Claims. 1 My invention relates to arrangements for separatingparticles of different mass from mixtures thereof and, in particular,relates to an arrangement for separating isotopes of the chemicalelements. Its operation depends upon a particularly effective method ofimparting widely different velocities to particles of even very slightlydifferent mass, and then utilizing the difference in velocity foreffecting physical separation of the particles.

One object of my invention is, accordingly, to provide a novelarrangement and method for separating, from mixtures thereof, particleswhich differ from each other in mass.

Another object of my invention is to provide a novel and improvedarrangement and method for causing electrified particles havingdifferent masses to be physically separated from each other.

Still another object of my invention is to provides, novel and improvedmethod of producing widely different accelerations between particleshaving masses which differ from each other.

Another object of my invention is to provide a novel arrangement andmethod for producing widely different velocities as between ions havingonly slightly different masses.

A further object of my invention is to provide a novel arrangement andmethod for segregating from mixtures thereof different isotopes of thesame chemical element.

Other objects of my invention will become apparent upon reading thefollowing description, taken in connection with the drawings, in whichthe single figure is a diagrammatic showing of one form of apparatus inwhich the prin-' ciples of my invention may be embodied;

Referring in detail to the drawings, a vacuum-tight chamber I may beconsidered to be subdivided into five different chambers 2, 3, 4,

chamber 5 and the ion-collecting chamber 6 may conveniently be ofconducting material.

The chamber 2 is provided at one end with an y em ss e gaih d o any typThe walls} known in the art to be suitable as a source of a concentratedelectron beam. The chamber 2 is likewise provided with an offtake 9 to avacuum pump of sufficient capacity to maintain the desired vacuum in theabove-mentioned system of chambers, even when a desired quantity ofgaseous ions is allowed to flow into the chamber in the immediatevicinity of the cathode 8 through a duct ll leading from a reservoir ofmolecules of the substances which it is desired to separate from eachother. In front of the cathode 8 there is provided a series ofdiaphragms l2, l3 and M of a type known in the art to be suitable forproducing a concentrated beam of ions or other charged electricalparticles; The diaphragms l2, I3 and I4 are connected to a suitablesource [5 of direct-current potential which has one ter-" minalconnected to the cathode 8 and also, preferably, to ground. The wall ofthe chamber 2 opposite to the end containing the cathode 8 is piercedwith an aperture which is aligned with similar apertures in the platesl2, l3 and 14. It will readily be evident that if the diaphragm I2 ispositive relative to the cathode 8, electrons will be accelerated in thespace in front of the latter, and that these will ionize any moleculeswhich have been allowed to flow into the chamber 2 through the duct ii.If the diaphragms l3 and M are negative in potential relative to theoathode 8, they will accelerate positiveions thus produced by theelectron stream along a path passing through their apertures and throughthe aperture in the end wall of the chamber 2 which is adjacent thechamber 3.

A high negative potential is imparted to the chamber 3 relative to thecathode 8, and the end wall of the chamber 3, which is adjacent thechamber 2, is provided with an aperture which is aligned with theapertures in the diaphragms l3 and I4. Such a system of electricalpotentials will produce a narrow beam of positive ions accelerated to ahigh velocity which will pass into the interior of the chamber 3. Whereit is desired to produce a stream of negatively charged ions ornegatively charged electrified particles,

it will be obvious to those skilled in the art that the potentials ofthe diaphragms l3 and I4 and chamber 3 and provided with a pair ofapertures I1 and 18 in its end walls which are aligned with theapertures in the diaphragms l3 and i4 and in the end walls of thechambers 2 and 3, as abovedescribed. A narrow space intervenes betweenthe respective end of the cylinder 16 and the adjacent end walls of thechamber 3, and a source of alternating potential-"2| which.may; ion (EX-ample, have. an amplitude of 1000-volts: and a frequency of 70 me. persecond, is connected between the cylinder l6 and the chamber sub--stantially at one end thereof 3. It will be evident from the foregoingdescription that an alternating voltage will be set up in the" spacesbetween the end walls of the cylinder-16: and:

those of the cylinder 3, but thatthe'spaceinthe.

interior of the cylinder l6willabevirtually an:

electric-field-free space in which any electrified particles enteringthrough theapertures in one end of the cylinder [6 will move withoutacceleration or deceleration until they pass. through the aperture inthe opposite end of the cylinder I6.

The endwall-of the chamber 3, which .is .remote from the chamber2,.isprovided withanaperture aligned witht-he-apertures l1 and; i8, andthe above-described-arrangement will be seen. to be such thata beam.of..elect'rifiedparticles emanating in. front: of the cathode 8' will"be. passed throughthe aperturesimthe. diaphragms i3 and. M, theapertures ILa-ndJa andintothe interior of the decelerating: chamberAl.The. end wall of the chamber 4,, which is. adjacent. the. chamber. 5, isoLmetal. andis. provided witl'ran. aperture 22.- which. is. alignedwith.the. apertures l1 and 3.. This end. wall. is-..impressed'.by. a suitablevoltage source:.(not.shown) with; a.negative voltage: which ismuchrlower. thanthat :irnpressed on. the: chamber. 3.. It will. be.seen. to result from this arrangement that theelectrifiedparticles inthe above-mentioned beam-willlpass. through the aperture: zzfwith amuch:lower-veloc ity'than that which .they' possessedwhile. passing.

through. the cylinder "5-.

The electrifiedparticles,-. when about to pass through the:apertures-in. the: end. wall. or. thechamber. 3 whichis adjacentrthe;chamberfi, will.-

have a kinetic energy. corresponding-.to-theproduct of. theirelectrical. charge by; the voltage-0f: the cylinder 31relative: tothecathode 8.: Since. the electrical charge produced on ions. in .front ofthe cathode 8'-will,- inegeneral be the same even though. the ions.differ. fromreach other in. mass, thevelocities oithe. ions whenthey.enter the chamber 3s wilLbe. inversely. proportionaLto the square rootsof their respective masses. How.- ever, one of the principal problemsto.be. solved by my above-described arrangement'lissthe separation of ions;such. as isotopes. of the: same.- element, which. differ from. each:other. only slightlyin mass. In such cases;.the. velocity .oiionsof'.each particular. isotope. will.be.-.the same,. and.

the velocity. of.difierent.isotopes wilL. diffier from. each other onlyslightly,.the-velocitiesofldifferent. isotopes. being: inverselyproportionalto the square root. of their respective masses.

In the space betweenthe'end wallotthe chambar 3 and the adjacentaperture |'|-,the iOIlSIWill be subjected to an alternatingelectricfieldhav ing the frequency of the source Ziwhich williurtheraccelerate or; decelerate-themin. an. amount dependingupontheinstantaneeusvalue: and sign of this electricfield. The ionswilllthen pass through the field-freespace. alongthe-axisoi. the. cylinder l6andwill arriveat the aperture. (8 with the same velocity that theyhadon.leaving. the aperture] 1-. However, thetime. at mhthey arrive at theaperture l8 will obviously depend upon the respective velocities withwhich they pass through aperture I1, and as has just been stated above,this velocity will difier for isotopes of different mass, and will alsodiffer even as between .isotopes-. o the .same.-mass which pass throughtheraperture [hat different'times in the cycle of the voltage impressedby the source 2|.

The source 2| impresses an electric field on the space between theaperture l8 and the aperture iF-w-hibh iseXactIy eQual and in the samedirection as'the electric field impressed on the ions just. before: theypass; through the aperture l1. Asa resnlt eachaion will leave theaperture 19 with arvelocity-which depends upon the relativephasertofTthe electric field between the apertures l8 and .IQ and .theelectric field in front of the aperture IT at theinstant of passing; andthis relative phase will depend in turn on the time consumed by the iontraversing the distance from the. aperture ilto .the aperture. Hi. Inaccordancewith the.foregoingconsiderations.the length of thechamber3.-is;.selected-..to be. substantially equal to. the. lengthof axhalf-integral. number of cycles...of-.the'-frequencyof'the source 2| so thatitispossible.to.causeionshavingrthe mass of one isotope to.traverseithe. distance between. the apertures. l1;- and..l.8..in...some' half-integral number; oilcycl'esoithe' source 2.1';.-b'ut,. on the other hand, electrifiedparticles, such as otherisotopes.

havingmasses which .difierirom that of the firstmentionedisotopewilllhave. different velocities in. passing throughtithe: chamber. 16and will correspondingly enterthe. electric held. between apertures.18.. andimlwhenrthe latter hasa difierent phase. .f'romthat of-l theelectric field; in front. of. theiaperture ll'whenthey pass throughit... Thus, .,thei.ions; of. the. selected. isotope first mentioned willenter the decelerating chamber 4 withthesamevelocity.thattheyhadinentering the. chamber 3.; .but..alll other isotopes will .havedifferentvelocities. from those that. they. had. in entering the chamber3. The. effect. of. the. passage through the chamber 3 is thus todifferentiate from. each. other. the. velocities. oi. differentisotopes, or other.electricaLparticles. having identical chargesbut.difierenti masses.

Within the decelerating, chamber 4, the. electrified. particles.aresubjected to .an-electric field whichrtends to greatly slowthemdcwn,nearly but. not quitert'o zero. velocity.-. It can beshown.

that the residual velocities...with.. whichthe par..- ticles. passthrough..-the aperture. 22' will. differ very. greatly. as. between.isotopes or. other. particles of. evenslightly; diiierent mass.

. After, passing. throughthe. aperture. 22, the particles. pass.through; amagneti'c. field. of con: stant' magnitudewhich.isperpendicularto. the direction. inwhich. they. are. moved; Sucha magneticfield. will..cause..moving. particles. to be deflected.intdcurvedlpathsthe curvature of. the.

pathdepending upon. the velocity. with which.

they are. moving. aswell; asmtheir. masses. Thus, twoisotopes. passingthroughthe aperture 22, even. if..of nearly the same...mass,,wi1l.have,..in accordance with. the foregoing description, widely,different. velocities and. will. correspondingly. follow. paths. of:widely different. curvature inthechamber. 5. Thecollecting; chamber 6 isprovided .with.anaperturecorresponrling inposition. torthe. path.followed. by. the. isotope which it is desired. to collect All. such.isotopes will, therefore, pass. intothe collecting chamber. 6, whileallother isotopesor charged electrical particles will be seatteredabout. onthe walls ofthe chamber 5 or on the exterior walls chamber 6.

Since the velocity with which two difierent isotopes pass throughcylinder 16 is, as'above stated, inversely proportional to the squareroot of their respective masses, the time they consume in passing fromthe aperture H to the aperture 18 will be proportional to the squareroot of their respective masses. It is obviously possible to so selectthe frequency of the source 2| that the time thus consumed by thedesired isotope is an odd number of half periods of the source 2|, butthe time consumed by an undesired isotope is an even number of halfperiods of, the source 2|. Under such circumstances,

of the the velocity with which the first isotope passes through theaperture I9 is the same as that with which it entered the chamber 3, butthe velocity with which the undesired isotope enters the aperture [9 isless than that with which it entered the chamber 3 by an amountcorresponding to twice the alternating voltage of the source 21. Thisaffords an effective means of Widely differentiating the velocities ofegress of two. isotopes, or other electrically charged particles,entering the chamber 3 with substantially identical velocities.

While I have described an arrangement in which the number of ionspassing through the apertures in the diaphragms I3 and I4 issubstantially constant with time, it is also within the scope of myinvention to pulse the voltage impressed on the diaphragm i2 relativetothe cathode 8 at the same periodicity as that of the source 2 l, orotherwise to modulate the ion beam. The phase of such pulses relative tothe source 2| should be made such that an undesired isotope will neverenter chamber 3 at a time when the voltage impressed by the source 21 iszero. By the expedient of pulsing the ion beam, it is possible to insurethat the net velocity change suffered by an undesired isotope in passingthrough the alternating fields at the opposite ends of cylinder l6 has adesired value, since the phases of both the alternating electric fieldsthrough which the particle passes are fixed and predeterminedquantities.

I claim as my invention:

1. In combination with a means for producing a beam of movingelectrified particles, means for passing said particles consecutivelythrough two alternating electric fields, means for decelerating by-apredetermined amount said particles after passing through the second ofsaid fields, and means for separating from each other such of saidparticles as have different velocities after said deceleration.

2. In combination with a source of electrically charged particles, meansfor establishing an electric field having a direct-current component andan alternating-current component for accelerating said particles to arelatively high velocity, means providing a field-free space traversedby said. particles subsequent to said acceleration, means fordecelerating said particles by an electric field having a direct-currentcomponent slightly smaller in magnitude than said directcurrentcomponent of said first electric field, and having an alternatingcomponent of substantially thesame frequency and magnitude as saidalternating component of said first electric field,.the directions ofall said electric fields being substantially parallel, and means forseparating said particles in accordance with their respective vetricfield.

3. In combination with a source of electrically charged particles, meansfor establishing an electric field having a direct-current component andan alternating-current component for accelerating said particles to arelatively high velocity, means defining a field-free space traversed bysaid particles subsequent to said acceleration, the time spent intraversing said field-free space being some odd number of halfperiods ofsaid alternating current, means for decelerating said particles by anelectric field having a direct-current component slightly smaller inmagnitude than, and opposed to, said direct-current component of saidfirst electric field, and having an alternating component ofsubstantially the same frequency and magnitude as said alternatingcomponent of said first electric field, the directions ofall saidelectric fields being substantially parallel, and means for separatingsaid particles in accordance with their respective velocities afterpassing through said second'electric field.

4. In combination with a means for producing a beam of movingelectrified particles, means for passing said particles consecutivelythrough two substantially cophasal equal alternating electricfields-which are substantially parallel to the direction of motion ofsaid particles, means for decelerating by a predetermined amount saidparticles after passing through the second of said fields, and means forseparating from each other such of said particles as have differentvelocities after said deceleration.

5. In combination with a means for producing a beam of movingelectrified particles, means for passing said particles consecutivelythrough a first alternating field, a field-free space and a secondalternating field, said alternating fields being substantiallysynchronized and having substantial components parallel to the directionof motion of said particles, the time spent in traversing saidfield-free space being some integral number of half-periods of saidalternating fields.

6. In combination with a means for producing a beam of movingelectrified particles, means for passing said particles consecutivelythrough a first alternating field, a field-free space and a secondalternating field, said alternating current fields being synchronizedand having substantial components parallel to the direction of motion ofsaid particles, the time spent in traversing said field-free space beingsuch that said alternating current fields respectively produce changesof velocity which are substantially equal but of opposite algebraic signin certain of said particles.

'7. In combination with a means for producing a beam of movingelectrified particles, means for passing said particles consecutivelythrough two substantially cophasal equal alternating current fieldswhich are substantially parallel to the-direction of motion of saidparticles, and means for separating from each other such of saidparticles as have different velocities after passing through said twoalternating electric fields.

8. In combination, means for producing a rapidly moving stream ofelectrified particles, a first chamber having conductive walls, a second'chamberhaving conductive walls insulatingly een thrones sa d secondchamb r, readies electrode for said particles outside said fii stghan i:means i9 intere ting h fill fi i ih l p o ntia d a e qe V ves th ax s.be en s id fir t air of anert i esend i -rimrr s as a subt tial cor asalnd e ua alt iaa sch m tial difierencealong the agi s; between saidsecond p ir f p ures.

9- In o ination. mean o P e ne rapidly v n tr m. le tr fi d a ticl s fih mb r hav n conduc i Wa a ec n cham e ha in c ndi ir W s nsu i s v supprted wi hin a first ch mb a firs pa per e al ned ith sai b a n h especive wallsf aid first an econ c amb rs, a secon pa r ofa r res nthe wll-s i: t sa two ham ers and ali ned w th the P Of sa d beam throu hsaid second ch mber, me ns for parati g sai artic s. of d f er ntvelocity after thei issue through said second pair of apertures, areceiver electrode for said particles out side said first chamber, andmeans for impressing an alternating acceleration on each particle as ittraverses said first pairof apertures and for impressing analternating.acceleration of substantially equal and opposite magnitudeon said particle as it traverses said second pair of apertures.

10. In combination, means for producing a rapidly moving stream ofelectrified particles, 2. first chamber having conductive walls, asecond chamber having conductive walls insulatingly supported withinsaid first chamber, a first pair of apertures aligned with said beam inthe respective walls ofsaid firstand second chambers, a second pair-ofapertures in the walls of the said two chambers and aligned with thepath of said beam through said second chamber, means for separating saidparticles of different velocity after they issue through said secondpair of apertures, a receiver electrode for said particles outside saidfirst chamber, means for impressing an alternating acceleration on eachparticle as it traverses said first pair of apertures and for impressingan alternating acceleration of substantially equal and oppositemagnitude on said particle as it traverses said second pair ofapertures, and means for applying a decelerating force to the particlesof said beam after they issue from said second pair of apertures.

11. In combination, a first cylindrical chamber having conductive walls,and coaxial therewith a second cylindrical chamber having conductivewalls positioned inside said first chamber, the end walls of said secondchamber being separated from the end walls of said first chamber byrelatively narrow gaps and said second chamber being insulatinglysupported within said first chamber, a first pair of apertures in onepair or adjacent end walls of said chambers, a second pair of aperturesin the other pair of end walls of said chambers, all said aperturesbeing positioned on the common axis of said chambers, means forimpressing an alternating voltage between said two chambers, means forprojecting a stream of electrified particles along the common axis ofsaid two chambers, and a receiver electrode for said electrifiedparticles which have passed through said second set of apertures.

12. Incom'bination, afirst cylindrical chamber having conductive walls,and coaxial therewith a second cylindrical chamber having conductivewalls positioned inside said first chamber, the end walls of said secondchamber being separated from the end walls of said first chamber byI813:-

i-re n r o s ts nd. ai set edchar e being msaiseugiy supported withinsaid st chamber, a first pair of apertures in one, pair of adjacent endwalls of said chambers, a second pair of apertures in 'the other pair ofend walls. of said chambers, all said. apertures being positioned on thecommon axis of'said chambers, means for impressing an alternatingvoltage'b'e tween said two chamber'sQmeanS for. projecting a stream ofelectrified particles along theconimon axis of said two chambers, and,meansfor separating particles of different velocities 'i'iisaid streamafter they have issued f roin said second pair of apertures. V v

13. In combination, a first cylindrical chamber having conductive walls,and coaxial therewith a second cylindrical chamber havin wnductive Wallspositioned inside said first chamber, the d w l f aid se nd chamb beingsep ate from the end walls of said first chamber. b relatively narrowgaps and said second chamber being ins ti s up t d W th n sai firstchamber, a first pair of apertures in one pair of adjacent end Walls ofsaid chambers, a second pair of apertures in the other pair of end wallsof said chambers, all said apertures being, 1305i tioned on the commonaxis of said chambers, means for impressing an alternating voltagebetween said two chambers, means for projecting a stream of electrifiedparticles along the common axis of said two chambers, means for applyinga decelerating force to said electrified particles after they havepassed through said second pair of apertures, and means for separatingfrom each other such of said particles as have different velocitiesafter being subjected to said decelerating force.

14. Apparatus for separating from each other electrified particleshaving substantially equal electric charges, but difierent masses whichcom.- prises means for, accelerating said particles by means of a firstelectric field having a directcurrent component and an alternatingcurrent component, said direct-current component con sisting ofintermittent pulses having the same frequency as saidalternating-currentcomponent, a region substantially tree irornaccelerating or decelerating forces disposed in the path of saidparticles, means for subjecting said particles to a second electricfield having a direct-current component slightly smallerthan and opposedt0 said direct-current component of said first field and having analternating component of sub stantially the same amplitude and frequencyas said alternating component of said first electric field, thedirections of all said electric fields being substantially parallel, andmeans for separating from each other particles having differentvelocities after passing through said second electric field.

1.5. In combination with a stream of charged particles having difierentvelocities, means for imparting to said particlesa periodieaccelerationin a direction parallel to their reassess path traversed by saidparticles afte r s'a id acceleration which is substantially free fronijforc'e s producing acceleration in said direction and which has a lengthsuch that some of said particles traverse it in a time substantiallycanal to a half-period of said periodic "acceleration, and means forimparting to said particles'a periodic deceleration in said directionwhich is substantially equal and opposite'to'said periodic acceleration.

16. Means for separating from each other electrified particles havingequal electric charges and difierent masses which comprises acceleratingthe particles of desired mass to a predetermined speed, passing themconsecutively through two electric fields oscillating at the same highfrequency and spaced apart within a resonant cavity which resonates atsaid frequency; the fields being of such strength, dimensions andspacing relative to each other that particles traversing the said fieldsat the predetermined speed will undergo substantially equal changes oftheir velocities but of opposite algebraic sign, and means forseparating from each other particles having different direction or speedof motion after passing through the second electric field.

WILLIAM ALTAR.

10 REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Name Date Sloan July 30, 1935 OTHER REFERENCESNumber

